The rates of the reactions of the colored para-substituted phenylacetonitrile anions 1a−c and the phenylpropionitrile anions 2a−c with Michael acceptors (3a−u) were determined by UV−vis spectroscopy in DMSO at 20 °C. The reactions follow second-order kinetics, and the corresponding rate constants k2 obey the linear-free-energy relationship log k2(20 °C) = s(N + E), from which the nucleophile-specific
Basicities and Nucleophilicities of Pyrrolidines and Imidazolidinones Used as Organocatalysts
作者:Feng An、Biplab Maji、Elizabeth Min、Armin R. Ofial、Herbert Mayr
DOI:10.1021/jacs.9b11877
日期:2020.1.22
the attack of the amines at the electrophiles to be determined. The resulting second-order rate constants k2 followed the correlation log k2(20 °C) = sN(N + E), where electrophiles are characterized by one parameter (E) and nucleophiles are characterized by the two solvent-dependent parameters N and sN. In this way, the organocatalysts A1-A32 were integrated in our comprehensive nucleophilicity scale
Nucleophilicity Parameters of Pyridinium Ylides and Their Use in Mechanistic Analyses
作者:Dominik S. Allgäuer、Peter Mayer、Herbert Mayr
DOI:10.1021/ja407885h
日期:2013.10.9
derive the nucleophile-specific parameters N and sN for these ylides. Pyridinium substitution is found to have a similar effect on the reactivity of carbanionic reaction centers as alkoxycarbonyl substitution. Agreement between the rate constants measured for the 1,3-dipolar cycloadditions of pyridinium, isoquinolinium, and quinolinium ylides with acceptor substituted dipolarophiles (arylidenemalononitrile
吡啶鎓、异喹啉鎓和喹啉鎓叶立德与二芳基碳鎓离子、醌甲基化物和亚芳基丙二酸酯(参比亲电子试剂)在二甲基亚砜溶液中的反应动力学已通过紫外-可见光谱进行了研究。发现二阶速率常数 (log k2) 与参考亲电试剂的亲电性 E 线性相关,如线性自由能关系 log k(20°C) = sN(N + E) (J. Am. Chem. Soc. 2001, 123, 9500),这使我们能够推导出这些叶立德的亲核试剂特异性参数 N 和 sN。发现吡啶取代对碳负离子反应中心的反应性具有与烷氧基羰基取代相似的影响。吡啶鎓、异喹啉鎓、异喹啉鎓的 1,3-偶极环加成反应的速率常数之间的一致性 和喹啉叶立德与受体取代的偶极体(亚芳基丙二腈和取代的查尔酮)以及从 E、N 和 sN 计算的那些表明,上述相关性也可用于预测逐步或高度不对称协调环加成的绝对速率常数。计算和实验速率常数之间的偏差达 10(6) 倍,表明反应机制发生了变化。
Nucleophilic Reactivities of Imide and Amide Anions
作者:Martin Breugst、Takahiro Tokuyasu、Herbert Mayr
DOI:10.1021/jo1009883
日期:2010.8.6
1994, 33, 938−957), allowing us to determine the nucleophilicity parameters N and the nucleophile-specific parameters s for these nucleophiles. The reactivities of all sulfonamide and diacylimide anions are found in a relatively small range (15 < N < 22). Comparison with structurally related carbanions revealed that amide and imide anions are less reactive than carbanions of the same pKaH. These effects
在DMSO和乙腈溶液中,通过紫外可见光谱研究了酰胺和酰亚胺阴离子2a - o与二苯甲基铵离子1a - i和与结构相关的醌甲基化物1j - q的反应动力学。二阶速率常数(日志ķ 2)与亲电性参数线性相关ë的1A - q根据相关日志ķ 2 =小号(Ñ + ë)(Angew化学,诠释埃德英格兰。。。1994年,33(938-957),这使我们能够确定这些亲核试剂的亲核参数N和亲核试剂特异性参数s。发现所有磺酰胺和二酰基酰亚胺阴离子的反应性都在相对较小的范围内(15 < N <22)。与结构相关的碳负离子的比较显示,酰胺和酰亚胺阴离子的反应性低于相同p K aH的碳负离子。这些作用可以归因于酰胺或酰亚胺阴离子中孤对之一的不存在共振稳定作用。由于酰胺和酰亚胺阴离子仅在氮原子上受到苄鎓离子的攻击,因此必须修改科恩布鲁姆对酰胺阴离子的环境反应性的解释。
N-Heterocyclic Carbenes: Organocatalysts with Moderate Nucleophilicity but Extraordinarily High Lewis Basicity
作者:Biplab Maji、Martin Breugst、Herbert Mayr
DOI:10.1002/anie.201102435
日期:2011.7.18
Unique organocatalysts: Arduengo's carbenes 1 and 2 are 103 times more nucleophilic than the Enders carbene 3, which attacks electrophiles with similar rates as diazabicyclo[5.4.0]undecene (DBU) and 4‐(dimethylamino)pyridine (DMAP). The unique organocatalytic activities of 1–3 are explained by their extraordinarilyhighLewisbasicities, which exceed those of PPh3, DBU, and DMAP by more than 100 kJ mol−1